Engineering Solvent-Anion Interactions via Asymmetric Ethers for 200 Wh Kg^-1 Low-Temperature Anode-Free Sodium Pouch...

Achieving highly reversible Na plating/stripping is crucial for the stable operation of low-temperature anode-free sodium metal batteries (LT-AFSMBs), yet simultaneously realizing ultra-high Coulombic efficiency (CE) and long-term durability, accompanied by high energy density, remains a formidable challenge. Herein, by regulating the molecular side chain, we design an asymmetric chain-like ether solvent that elegantly balances weak Na⁺-dipole and strong anion-dipole interactions. This rationally tailored electrolyte fosters an anion-rich Na⁺ coordination environment, which significantly lowers the desolvation barrier and drives the formation of a robust, anion-derived solid electrolyte interphase with rapid interfacial dynamics. Consequently, the optimized electrolyte delivers an unprecedented average CE of 99.96% over 500 cycles at -20°C. Remarkably, even under stringent conditions of an ultra-high cathode loading (28.05 mg cm^-2) and areal capacity (2.48 mAh cm^-2), the LT-AFSMBs retain 85.9% of their initial capacity over 600 cycles at -20°C. Moreover, practical Ah-level anode-free pouch cells demonstrate stable operation for 300 cycles, yielding a high energy density exceeding 200 Wh kg^-1 (based on the mass of entire pouch cell). This paradigm-shifting solvation strategy provides a highly viable and scalable blueprint for the next-generation, extreme-temperature energy storage systems.